/Engine/Source/Runtime/WebBrowser/Public/SWebBrowserView.h
This method has to be called asynchronously by passing a callback function, which will be called at a later point when the result is ready.
void GetSource ( [TFunction](API\Runtime\Core\GenericPlatform\TFunction)< void(const [FString](API\Runtime\Core\Containers\FString) &)> Callback ) const